So far I got to say that I love this software, it really is a worthy replacement for Office. It looks modern (better than any free Office alternatives out there) and the fact that it has pretty much the same features as the current Office (collaboration and what not), I just have to recommend it to people.

However, they're a few things that the dev can consider.

1. Is it OnlyOffice or ONLYOFFICE? Cause, to be frank, I feel OnlyOffice looks more professional than an all caps name, and that very few apps actually use all caps.

2. Why does the iOS app name called Documents instead of OnlyOffice? Consistency please

3. Consider publishing on the MacAppStore as well, this will increase exposure and get more people to know the existence of such great software.

4. In regards to subscription issues if the app is on MAS, I would suggest you to look at how Amazon did it with their Kindle as they make the users go to Amazon website to subscribe, pretty sure you can do something like give the users a copy of OnlyOffice like how it's now and then have a pop up (like Pages, Keynote and Numbers) explaining the features, and that they can unlock more features (collaboration and etc.) when subscribed. Oh and make sure you have the checkbox don't show this again so you don't annoy your users.

5. The website could use some work as well, I understand that you offer the desktop version for free, but subscribing will unlock collaboration, mobile apps, cloud storage, additional modules and etc. And that there's also an option to host locally? All this is fine but I feel the website could do a better job at explaining these.